To wake the sleeping Snorlax in Pokémon Blue, you need to use a Poké Flute. This item is obtained after completing a quest in Lavender Town, where you rescue Mr. Fuji from Team Rocket in the Pokémon Tower.
Here’s a step-by-step guide:
Reach Lavender Town: Navigate through Rock Tunnel to get to Lavender Town.
Complete the Pokémon Tower Quest: Enter the Pokémon Tower and defeat the ghosts using the Silph Scope, which you acquire by defeating a Team Rocket Grunt in Celadon City.
Rescue Mr. Fuji: After reaching the top of the tower and defeating Team Rocket, you will rescue Mr. Fuji, who will then give you the Poké Flute.
Use the Poké Flute: Go to either Route 12 or Route 16 where Snorlax is blocking the way. Stand next to Snorlax, open your item menu, select the Poké Flute, and play it. This will wake Snorlax and initiate a battle123.
This is the only method available in Pokémon Blue to wake Snorlax, as there are no alternatives within the game mechanics.